Process for starting an operation to continuously cast metal rod

ABSTRACT

A starting process is disclosed for a system in which molten metal flows from a reservoir into a cooled forming die from which externally-solidified incremental lengths of metal are drawn to produce a continuous integral shape, e.g. rod. A starter length of hollow material is positioned in the forming die to receive the initial flow, which develops a tapered liquid-solid interface with the starter length. Externally-solidified incremental sections may then be drawn or cast.

'United States Patent [191 Frus [ 1 Sept. 23, 1975 I PROCESS FORSTARTING AN OPERATION TO CONTINUOUSLY CAST METAL ROD [75] Inventor:Larry D. Frus, Whittier, Calif.

[73] Assignee: Stoody Company, Santa Fe Springs,

Calif.

[22] Filed: July 23, 1973 [21] Appl. No.: 381,965

6,602,207 9/1966 Netherlands 164/83 Primary ExaminerJ. Howard Flint, Jr.

Assistant Examiner-Gus T. Hampilos Attorney, Agent, or FirmNilsson,Robbins, Bissell, Dalgarn & Berliner [57] ABSTRACT A starting process isdisclosed for a system in which molten metal flows from a reservoir intoa cooled forming die from which externally-solidified incrementallengths of metal are drawn to produce a continuous integral shape, e.g.rod. A starter length of hollow material is positioned in the formingdie to receive the initial flow, which develops a tapered liquid-solidinterface with the starter length. Externally-solidified incrementalsections may then be drawn or cast.

10 Claims, 4 Drawing Figures VGA/TUE PUMP PROCESS FOR STARTING ANOPERATION TO CONTINUOUSLY CAST METAL ROD BACKGROUND AND SUMMARY OF THEINVENTION In general, difficulties encountered in continuouscastingprocesses include starting problems in addition to various productionfailures as by the billet freezing in'thc mold, breaking off, or thecontents of the mold becoming molten, to result in an external flow ofmetal. In spite of such failures, continuous-casting processes haveattained a relatively advanced state with regard to certain metals, e.g.aluminum and copper. However, efforts to continuously cast certain othermetals (for example high'tcmperature metals) particularly in lengths ofrelatively-small sectional size, have contin' ued to present significantproblems. One promising process has been developed wherein the rod orbillet being cast is drawn in a reciprocating motion pattern to bedeveloped as incremental sections. However, considerable difficultieshave been experienced in starting the process in view of the variouscritical states that are involved. I

In general, the present invention is directed to a process forinitiating a continuous casting operation. Specifically, the system ofthe present invention involves the use of a hollow or tubular seed orstarting rod for accomplishing the critical starting condition that canbe perpetuated to continuously cast. Additionally, the starting rod, orthe like, isconditioncd as by an airstream to avoid such problems ascondensation.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which constitute apart of this specification, an exemplary embodiment exhibiting variousobjectives and features hereof is set forth, specifically:

FIG. I is a diagrammatic view of a casting system for use in accordancewith the present invention; and

FIG. 2 constitutes a series of fragmentary sectional views through thedie portion of the system of FIG. 1 which are illustrative of theprocess of the present invention.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT As required, a detailedillustrative embodiment of the invention is disclosed herein which isrepresentative of the best mode within the purview of present knowledgefor that purpose. The embodiment exemplifies the invention which may, ofcourse, be constructed in accordance with other forms and steps, some ofwhich may be radically different from those disclosed herein. However,the specific structural and process details disclosed are representativeand provide a basis for the claims which define the scope of the presentinvention.

Reference will be made initially to FIG. I, for a consideration of acontinuous casting process to which the present invention is applicable.There is shown a fur nace F for providing molten metal to a cooled diestructure D. In the operation of the system, molten metal entering thedie structure D is externally solidified (adjacent the die walls) sothat it may be drawn in a rod form from the die structure D by awithdrawal roller mecha nism R. A drive unit U actuates the rollermechanism R in a manner so that the billet or rod B (or other de siredlinear casting) is drawn from the die structure D in anintermittent-motion pattern. That is, a length of rod B which has beenexternally solidified in the die structure D is drawn in what might betermed a forward drawing or withdrawal stroke. Then following eachwithdrawal stroke, the roller mechanism R is actuated by the unit U toaccomplish a reverse movement or abbreviated return stroke of the rod Bto compensate for shrinkage resulting from solidification of the metaland to preserve the rod B integral so as to accomplish a continuousshape. The motion pattern of the rod B is critical and is one of theelements of accomplishing the desired integral product.

Considering the structure of FIG. 1 in somewhat greater detail, thefurnace F contains a mass 12 of molten metal for supplying the desiredcontinuous rod B. Specifically, the mass 12 is contained in a crucible14 of refractory material which is somewhat upright and defines a bottomoutlet passage 16 from which molten metal flows to develop the rod B. Aninduction coil 18 is provided about the crucible I4 and is connected, aswell known in the art, to an electrical power source 20. of course, anexternal housing, as well known in the art, may be provided for thefurnace F outside of the coil 18.

Molten metal flowing from the reservoir mass 12 through the passage 16is received in a generallycylindrical casting cavity 22 of the diestructure D. The cavity 22 is generally coextensive with the passage 16.As illustrated, the cavity 22 is concentric within a hollow annulus 24through which coolant 26, e.g. water, is circulated. Specifically, anintake duct 28 receives coolant from a source (not shown) which coolantcir culates through the annulus 24 and exhausts through an outlet duct30. Recognizing that a variety of specific arrangements and materialsmay be employed, in one embodiment the annulus 24 has been formed of analloy that is primarily copper. Accordingly, hightemperaturecapabilities exist along with good heattransfer characteristics.

As indicated above, it is to be understood that the rod B is drawn in acontinuous integral form section-bysection from the die structure D byengagement with a roller mechanism R including a pair of pinch rollers34 and 36. Of course, the rollers 34 and 36 may be variously supportedfor rotation and in that regard, the roller 34 is driven while theroller 36 functions as a backup of idler. The roller 34 is connected (asindicated by a dashed line 38) to the drive unit U for accomplishing thedesired reciprocating motion pattern. That is, the unit U actuates theroller 34 to draw a lengthof the rod B from the die structure D during adrawing stroke, then moves the rod B in a lesser reverse or returnstroke to preserve integrity with the liquid phase and compensate forthe shrinkage in the metal resulting from solidification.

In view of the above pertinent considerations, the system of the presentinvention may now be best understood by describing the sequence of themethod. Accordingly, assume initially that the molten mass 12 has notyet been placed in the crucible I4 (functioning as in a holding furnace)or, alternatively, that in an alternate structure a gate (not shown) isclosed, inhibiting the flow of molten metal through the passage 16.

Prior to the passage of molten metal into the casting cavity 22 (FIG.2a) and in accordance herewith, a seed section or hollow elongatedstarting rod 40 is positioned in the die structure as illustrated. Therod 40, as indicated is an elongated member of uniform cross section andideally comprises a composition that is compatible to that of the moltenmass 12. That is, the two compositions (e.g. cobaltnickel alloy andstainless steel) should have good weld bond characteristics toeffectively join together. One end 42 of the hollow rod 40 is positionedto lie well within the casting cavity 22 as illustrated. The passage 44(through the rod 40) extends to an opposed end 46 which is received in aventuripump 48. A radial bore 50 is provided contiguous to the end 42 ofthe rod 40 in the cavity 22. A stream of air is drawn through thepassage 44 (arrow 51) to avoid condensation of moisture in the diestructure D and the tube 40, and to preheat these elements (diestructure D and seed tube 40).

When the molten mass 12 (FIG. 1) attains the desired castingtemperature, flow is initiated into the cavity 22 (FIG. 2a). At thattime, molten metal enters the passage 44 (substantially cooler) and aliquid-solid interface is developed, resulting in a configuration thatsimulates a stage in the casting process, deemed to be somewhat asillustrated in FIG. 2b. Certain of the molten metal flowing into thepassage 44 solidifies and is welded to the starter rod 40 while the rodalso provides an' initial artificial metal skin 55 or solid exterior. Itis also noteworthy that as the molten metal enters the starter rod 40,gases are permitted to escape through the bore 50 then serving as aventing port rather than as during the preliminary period when thefunction was to prevent condensation from taking place inside the dieand reducing the temperature of the rod 40.

Considering the subsequent operation of the system,

a reoccurring cycle is performed to develop incremental lengths of thecontinuous integral rod B. Specifically, from the condition depicted inFIG. 2b, a length or incremental section 52 of externally-solidifiedmetal is drawn from the casting cavity 22. Of course, the length 52 mayvary in specific instances; however, it is generally less than thelength of the casting cavity 22. The drawing stroke is indicated by anarrow 54 and is accomplished by the reciprocaldrive unit U (FIG, 1) andthe coacting pinch rollers 34 and 36. 7 At the conclusion of the drivestroke, a newly-formed incremental section 52 of the rod has been drawnfrom the casting cavity 22. Thereafter, the return stroke occurs duringwhich the section 52 is moved in a reverse direction as indicated by anarrow 58 (FIG. which motion compensates for the shrinkage ofsolidification within the metal.

Although some fine-adjustment deviations may be desirable, therelationship of the drawing stroke to the return stroke is somewhat inthe ratio of the volume of material drawn during a stroke, to the volumeof the shrinkage for that volume of material upon solidification.Gcnerally, the cross section of the rod B may be considered to besubstantially uniform. Consequently, the volume of the incrementalsection 52 provided dur' ing each drawing stroke is related to thelength of the stroke. Accordingly, the length of the return stroke isgenerally adjusted to coincide to the volumetric change of the castingmetal attendant solidification.

It may, therefore, be seen that the seed" tube or rod 40 as employedherein is effective to initiate a process which becomes continuous inthe sense that lengths of metal are produced increment-by-increment,passing as a continuous length from a die structure. Of course, variousspecific techniques may be involved; however, the steps of the presentinvention are described above and afford a basis for the claims as setforth below.

What is claimed is:

1. A starting process for the continuous casting of a solid rod ofmetal, wherein a stream of molten metal is flowed into a casting cavityto be cooled therein for horizontal movement in anexternally-solidified, continuous-length form through a passage fromsaid casting cavity, comprising:

placing a hollow section of solid metal horizontally disposed in saidpassage from said casting cavity; releasing said stream of molten metalto provide an initial flow of said molten metal to enter said hollowsection and become welded thereto; and

moving said hollow section of metal to withdraw out of said passage fromsaid cavity along with metal from said stream, to begin said process forthe continuous casting of a rod of solid metal.

2. A starting process according to claim I wherein said hollow sectioncomprises an elongated member of substantially-uniform cross section.

3. A starting process according to claim 1 wherein said stream of moltenmetal and said section of solid metal are of compatible compositions.

4. A starting process according to claim I wherein said molten metal andsaid section of solid metal are of compositions having weld bondcharacteristics to join each other,

5. A starting process according to claim I further including the step offorcefully passing an airstream through a portion of said hollow sectioncontiguous to said cavity and moving away from said casting cavity.

6. A starting process according to claim I wherein said hollow sectionof solid metal comprises an elongated hollow tubc defining a ventpassage therethrough.

7. A starting process according to claim 6 wherein said vent passageincludes a radial bore defined in said tube.

8; A starting process according to claim 7 wherein said hollow tube andsaid molten metal are compatible in that effective weld bonds existtherebetween.

9. A starting process according to claim 8 wherein said metal is movedfrom said casting cavity in discrete steps.

10. A starting process according to claim 1 wherein said metal is movedfrom said casting cavity in discrete steps.

1. A starting process for the continuous casting of a solid rod ofmetal, wherein a stream of molten metal is flowed into a casting cavityto be cooled therein for horizontal movement in anexternally-solidified, continuous-length form through a passage fromsaid casting cavity, comprising: placing a hollow section of solid metalhorizontally disposed in said passage from said casting cavity;releasing said stream of molten metal to provide an initial flow of saidmolten metal to enter said hollow section aNd become welded thereto; andmoving said hollow section of metal to withdraw out of said passage fromsaid cavity along with metal from said stream, to begin said process forthe continuous casting of a rod of solid metal.
 2. A starting processaccording to claim 1 wherein said hollow section comprises an elongatedmember of substantially-uniform cross section.
 3. A starting processaccording to claim 1 wherein said stream of molten metal and saidsection of solid metal are of compatible compositions.
 4. A startingprocess according to claim 1 wherein said molten metal and said sectionof solid metal are of compositions having weld bond characteristics tojoin each other.
 5. A starting process according to claim 1 furtherincluding the step of forcefully passing an airstream through a portionof said hollow section contiguous to said cavity and moving away fromsaid casting cavity.
 6. A starting process according to claim 1 whereinsaid hollow section of solid metal comprises an elongated hollow tubedefining a vent passage therethrough.
 7. A starting process according toclaim 6 wherein said vent passage includes a radial bore defined in saidtube.
 8. A starting process according to claim 7 wherein said hollowtube and said molten metal are compatible in that effective weld bondsexist therebetween.
 9. A starting process according to claim 8 whereinsaid metal is moved from said casting cavity in discrete steps.
 10. Astarting process according to claim 1 wherein said metal is moved fromsaid casting cavity in discrete steps.